Many industrial material fabrication processes involve melting, mixing and chemical reaction during material processing in an enclosed chamber. These processes are normally performed: at elevated temperature, which causes material to melt; with rotation elements, such as blades and/or screws, which provide the mixing mechanism. Materials can be polymers, polymer composites, metals, foods, or other materials in pellets, powder and liquid form. The chamber is normally made of metal such as steel, which is optically opaque.
Due to the complex geometry of the rotating elements and the complex properties and rheological behaviors of the materials encountered, the current understanding of the physics governing such melting, mixing and chemical reaction processes has remained insufficient. What hinders the understanding is the fact that operators could not see what was taking place in the chamber during melting, mixing and chemical reaction, especially when the feed material was changed from solid to the molten state. Direct viewing under active mixing actions is not convenient because the chambers are completely enclosed in metal and furthermore the rotation elements such as blades and screws are running. This is one of the main reasons that empirical approaches still dominate industrial melting, mixing and chemical reaction processes development and control.
In-line monitoring is an efficient way to overcome these difficulties. One would not only find out the state of the process, but also be able to use the data to correlate with the material properties such as the important product qualities. Conventional sensors such as temperature and pressure probes are normally used for such process monitoring; however, their response time is slow and the material properties cannot be directly monitored. The ultrasonic technique advantageously provides an ability to probe the interior of materials at elevated temperatures and pressures. It can be carried out non-destructively, non-invasively and in line.
However, because of the rotation and the odd shapes of the blades or screws which provide the necessary efficient melting, mixing and chemical reaction, synchronization between the ultrasonic measurement and the position of the rotating element, such as blades and/or screws, is required to track echo signals reflected from the rotating element in such a way that ultrasonic measurements can be done for nearly the same relative sensor-rotating element position.
Therefore, there is a need in industry for an improved ultrasonic apparatus and method for the monitoring of melting, mixing and chemical reaction processes.